Processes for the production of expanded polystyrene foam articles are known in the art. Thermoplastic beads, e.g., polystyrene beads, containing a blowing agent, normally hydrocarbon mixtures having a boiling point between about 80.degree. F. to 110.degree. F., are pre-expanded in a vessel by, e.g., introducing steam into said vessel or by controlled heating. After pre-expansion, the beads may be transferred directly to a mold cavity or, alternatively, they may be placed in a storage container before molding. After the molding step, foam articles may be stored in a drying room for a certain period of time.
N-pentane, or mixtures of n- and iso-pentane (up to about 25% iso-pentane by weight), is the most widely used blowing agent contained in the expandable polystyrene beads used as the raw material in the production of expanded polystyrene foam articles. In a conventional process of pre-expansion and molding, the blowing agent becomes separated from the expanded polystyrene beads and is lost into the surrounding atmosphere. U.S. Pat. No. 4,272,469 is representative of such processes forming expanded foam articles wherein the blowing agent (n-pentane) is removed from the polystyrene beads during pre-expansion and molding and is presumably allowed to escape into the surrounding atmosphere.
Where the initial blowing agent content of the expandable polystyrene beads is about 4-8 wt %, it has been determined that approximately 1-2 wt % of the blowing agent is lost during the pre-expansion stage, approximately 1-2 wt % is lost from the pre-expanded beads in closed storage bins, approximately 1-2 wt % is lost to the atmosphere during the molding cycle, and approximately 1-2 wt % is lost during aging and/or drying of the molded foam articles.